Apparatus and method for eliminating or reducing the internal flaws of semifinished products,especially at cast ingots,blocks,blooms,slabs,billets or the like

ABSTRACT

THE INVENTION DISCLOSES AN APPARATUS AND METHOD FOR ELIMINATING OR AT LEAST REDUCING THE INTERNAL FLAWS OF SEMIFINISHED PRODUCTS, ESPECIALLY AT CAST INGOTS, BLOCKS, BLOOMS, SLABS, BILLETS OR THE LIKE. THE INVENTIVE METHOD COMPRISES THE STEPS OF EXERTING A PRESSING FORCE AT ONLY PORTION OF AT LEAST ONE SIDE SURFACE OF THE SEMIFINISHED PRODUCT, AND COMPRESSING THE INNER PORTIONS OF THE SEMIFINISHED PRODUCT BY MEANS OF SAID PRESSING FORCE, SO THAT THE PORTIONS OF THE SEMIFINISHED PRODUCT WHICH HAVE NOT BEEN SUBJECTED TO THE PRESSING FORCE PROVIDE RESISTANCE AGAINST A CHANGE IN SHAPE OF THE SEMIFINISHED PRODUCT, AND THEREFORE, AT LEAST PARTIALLY PREVENT AN ELONGATION OF SUCH SEMIFINISHED PRODUCT. THE INVENTIVE APPARATUS FOR THE PERFORMANCE OF THE AFORESAID METHOD COMPRISES MEANS PROVIDING A PRESSING FORCE-EXERTING EDGE WHICH IS SMALLER THAN THE WIDTH OF THE SURFACE OF THE SEMIFINISHED PRODUCT.

Sept. 21, 1971 OLSSQN 3,606,785

APPARATUS AND METHOD FOR ELIMINATING OR REDUCING THE INTERNAL FLAWS 0FSEMIFINISHED PRODUCTS, ESPECIALLY AT CAST INGOTS, BLOCKS, BLOOMS, SLABS,BILLETS OR THE LIKE Filed Aug. 9, 1968 2 Sheets-Sheet 1 Fig. 7

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INVENTOR ERIK H. 0055011) BY WQ ATTORNEY P 1, 1971 E. A. OLS N 06,785

APPARATUS AND METHOD FOR ELIMINAT OR REDUCING THE INTERNAL FLAWS OFSEMIFINISHED PRODUCTS, ESPECIALLY AT CAST ING BLOCKS, BLOOMS, SLABS BILLETS OR THE LIKE 1 2 Sheets-Sheet 2 Filed Aug. 9, 19

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INVENT OR 81K 19- 01.55am

BY MMQ ATTORNEY United States Patent US. Cl. 72-199 5 Claims ABSTRACT OFTHE DISCLOSURE The invention discloses an apparatus and method foreliminating or at least reducing the internal flaws of semifinishedproducts, especially at cast ingots, blocks, blooms, slabs, billets orthe like. The inventive method comprises the steps of exerting apressing force at only portion of at least one side surface of thesemifinished product, and compressing the inner portions of thesemifinished product by means of said pressing force, so that theportions of the semifinished product which have not been subjected tothe pressing force provide resistance against a change in shape of thesemifinished product, and therefore, at least partially prevent anelongation of such semifinished product. The inventive apparatus for theperformance of the aforesaid method comprises means providing a pressingforce-exerting edge which is smaller than the Width of the surface ofthe semifinished product.

BACKGROUND OF THE INVENTION The present invention relates to an improvedapparatus for, and method of, eliminating or at least reducing theinternal flaws or defects of semifinished products, especially at castingots, blocks, blooms, slabs, billets or the like.

During the casting of semifinished products, especially ingots, blocks,blooms, slabs, billets or the like, whether such be by conventionalingot casting techniques or by a continuous casting process, differenttypes of internal defects or flaws oftentimes occur, primarily due tothe shrinkage occurring during solidification. Typical examples of suchare axial porosity, primaryand secondarypipe, which occur during thecasting of ingots formed of killed and semikilled steel, owing to anincomplete flow of the metallic melt into the shrinkage cavities orholes occurring during shrinkage. The rate of growth of the solidifiedlayer mainly reduces with increasing thickness or time-the thickness ofthe solidified layer S is approximately a function of the square root ofthe solidification time t, that is to say, S =f t-whereby, the verticalheat flow assumes practically no importance, and the solidificationfaces or fronts tend to approach one another with tapered or conicalmolds having a downwardly reducing acute angle. On the other hand, withapproximately parallel sides of the mold, the solidification faces orfronts can be approximately parallel at the top of the basin, andasymptotically approach the solidification center. In so doing, thestill liquid melt in the sump or basin transforms rapidly into amushy-like condition, and it can be readily understood that bridges canform which prevent ice the further flow of salt into the lower situatedhollow spaces formed by virtue of the contraction or shrinkage of thematerial.

During the casting of ingots it is attempted, on the one hand, toconsiderably suppress this phenomenon by using a conicity or tapering ofthe molds which is as large as possible but still economical andcompatible for the subsequent rolling operation; and on the other hand,to generally provide the molds with insulating and/or exothermic pouringheads. Even if these measures are carried out quite carefully, a portionof the weight of the ingot amounting to 8% to 18% still contains pipe tosuch an extent that it must be scrapped. In order to improve output,there is used, if the demands placed upon the final product permit, suchsteel production or casting techniques wherein there are cast ingots ofunkilled or semikilled steel, whereby instead of forming pipe at thecentral region of the ingot spaces or voids are formed inside thereofwhich, during subsequent rolling, must be welded together. However, thedanger always exists that, for instance owing to an oxidation of thebubbles prior to rolling or because of the collection of slag in suchbubbles, several of these bubbles will not be fused or Welded together.This again results in scrapping of the product. Other reasons for aninsufficient weld during the sub sequent rolling operation are too low atemperature or incomplete pressing.

Similar problems occur during continuous casting. With this techniquethere does not exist, as in the case of stationary or stand casting, thepossibility of improving the filling operation by providing a conicityor tapering of the strand. The formation of blowholes at the center ofthe strand is therefore extremely difficult to prevent.

There are, however, still other reasons why internal flaws or defectsoccur. The gases dissolved in the melt, but which tend to evolve orescape during solidification as the temperature drops, can result in theformation of bubbles. Furthermore, the contraction or shrinkage processleads to internal stresses, which can result in the formation of cracksor fissures.

Even if the above-mentioned hollow spaces, porosity or flaws, aregenerally welded shut by the subsequent rolling operation, provided thattheir surfaces are not oxidized, still it must be observed that aconsiderable reduction of the cross-section is necessary in order toobtain the cast material completely without defect or flaws. ln suchinstance, there must be performed a working or shaping operation which,depending upon the quality of the steel and the roller temperature,results in a reduction in the cross-section of 1:4 or even 1:10 of theoriginal cross-section. Under certain circumstances, for certain specialsteels, a still greater reduction may be necessary.

The reason why the cast ingots or blocks must be pressed together sostrongly until the porosity at the center is welded shut, can best beexplained in that with the conventional rolling techniques, the pressureexerted in radial direction upon the ingots or blocks is not completelyeffective to the desired extent at the central region. Thus, the appliedrolling or deformation work, for the most part, appears in the form ofan elongation or stretching, and possibly, also in a spreading orwidening of the material. While it is indeed possible, in order toprevent or limit the spreading of the material, to use a closed rollingpass, to thereby obtain an improved kneading at the center, suchtechnique has thus far provided only limited success.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of thepresent invention to effectively overcome the aforementioned drawbacksassociated with the prior art techniques.

Another, more specific object of the present inveniion relates to animproved apparatus for, and method of, eliminating or at least reducingthe internal flaws of semifinished products, especially at cast ingots,blocks, slabs, billets or the like.

Still a further significant object of the present invention is to carryout a pressing of the center of the ingot or strand which contains theflaws in such a way that the work employed for shaping or deforming doesnot primarily result in a stretching or widening of the material, rathercauses a flow of material which is directed more toward the inside.

Now, in order to implement these and still further objects of theinvention, which will become more readily apparent as the descriptionproceeds, the inventive method is generally characterized by thefeatures that the inner portions of the semifinished product arecompressed by applying a pressure to only a portion of at least one sidesurface of the semifinished product, so that the portions of thesemifinished product which are not subjected to such pressure provide aresistance against any change in shape and, therefore, at leastpartially prevent an elongation.

The inventive apparatus for carrying out the inventive methodaforedescribed utilizes means providing a pressing or pressure edge, thewidth of which is smaller than the width of the surface of thesemifinished product. According to one embodiment of the invention, thepressing or pressure edge is provided by means of a roller having a beaddefining such pressure edge, and the width of which head is smaller thanthe width of the surface of the semifinished product. Furthermore, anumber of rollers can be provided which at least partially enclose inform-locking fashion, the semifinished product.

BRIEF DESCRIPTION OF DRAWINGS The invention will be better understoodand objects other than those set forth above will become apparent whenconsideration is given to the following detailed description thereof.Such description makes reference to the annexed drawings wherein:

FIG. 1 is a cross-sectional view of a cast ingot;

FIG. 2 is a schematic representation of the rolling operation for aningot of the type shown in FIG. 1;

FIG. 3 schematically illustrates the rolling operation of FIG. 2, asviewed from the infeed side of the rolling mill;

FIG. 4 schematically illustrates the inventive method;

FIG. 5 is a sectional view taken perpendicular to the illustration ofFIG. 4;

FIG. 6 schematically illustrates a second variant of of the invention;

FIG. 7 schematically depicts a first embodiment of apparatus forcarrying out the inventive method;

FIG. 8 schematically depicts a second embodiment of apparatus forcarrying out the inventive method;

FIG. 9 illustrates in sectional view an ingot or block serving as thestarting material and is helpful in explaining the difference betweenthe previously conventional technique and the inventive method;

FIG. 10 shows the final condition of an ingot processed according to theprior art or conventional technique;

FIG. 10a is a sectional view taken perpendicular to the showing of FIG.10;

FIG. 11 shows the final condition of an ingot or block processedaccording to the teachings of the invention; and

FIG. 11a is a sectional view taken substantially perpendicular to FIG.11.

4 DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawings,in FIG. 1 there is depicted an ingot or block 1 having the blowholes 2at its center. According to FIGS. 2 and 3, this ingot 1 is guidedbetween the schematically illustrated rollers 3 and 4 of a rolling mill,thus subjected to a lengthening or stretching, indicated by referencenumeral 5, as Well as a widening or spreading, as indicated by referencenumeral 6 (FIG. 3).

The fiow of material has been schematically represented by two auxiliarylines a and b. Prior to engagement of the rollers 3 and 4, the auxiliaryline a extends perpendicular to the cross-section of the ingot 1. Owingto the internal friction of the material, during passage of the ingot 1through the rollers 3 and 4, the portions of the ingot at the region ofthese rollers 3 and 4 and in contact with such rollers tends to rust ormove ahead with respect to the central portionthis phenomenon has beenconveniently designated as a leadingor moving-ahead motion. The applieddeforming work primarily results in a stretching or elongation of thematerial which, in the first instance, occurs at that portion of thecross-section which is in contact with the rollers 3 and 4, and at theregion thereof. The internal material layers are entrained by theleading portions, but because of the resistance against deformation, theelongation at the center of the strand is smaller than in the outerlayers. Consequently, the original fiat cross-section as defined by theline a is deformed by the rolling operation and assumes the curved formof the line b and, specifically, in such a way that the edges lead theinner portion of the material, as shown.

Now, with the inventive method according to FIGS. 4 and 5, on the otherhand, only one portion of a side of a billet 1 of the like is pressed bymeans of a relatively narrow and rounded edge 10a of a tool 10. In sodoing, the non-pressed corner portions 7 and the portions 8 of theremaining sides of this billet 1 provide resistance against stretchingor elongation of the material as well as i also partially against aspreading or widening of such material.

According to a further improvement of the inventive method, as shown inFIG. 6, the non-pressed portions of the material of the billet 1 or thelike are enclosed in form-locking fashion in a form or mold 9 andpressed by means of a tool 10, so that a more pronounced compaction orcompression of the inner portions of the crosssection of the material isachieved.

According to- FIGS. 7 and 8, the inventive method can be carried out bymeans of a rolling operation. In FIG. 7, 'both of the rollers 13 and 14are provided with narrow beads .15 for pressing-in two oppositelysituated portions of the sides of a billet 1 or the like. The flanges orcollars 16 of the rollers 13 and 14 limit the width, that is thematerial flow in the direction of the roller axes. Also, in this case,the two sides of the billet 1 which have not been pressed in and thecorners of such billet prevent any appreciable lengthwise elongation, sothat the flow of material is primarily directed inwardly or forcedinwardly.

In the arrangement of FIG. 8 there are shown four rollers 20, eachhaving a press edge or bead 21, whereby the partial pressing of each offour sides of an ingot or block 1 or the like is possible. Whether it isdesirable to press in one, two or a number of sides, depends primarilyupon the configuration of the cross-section of the final product. Therollers 20 can be either driven or the ingot or the like can be pushedthrough between nondriven rollers or pulled through. If desired, thetools can synchronously move along with or follow a continuously movingcast strand.

According to the invention, the ingot or the like can also be cast topossess partial bulges or protruding portions at one or a number ofsides, which during pressing or rolling, while compacting the innerportions, can be pressed in. These bulges should only be so large thatthe portions which are not deformed by the tools or by the rollersprovide sufficient resistance against any elongation or against anyrushing ahead of the material as previously explained.

Also, within the framework of the invention, it is possible tosuperimpose upon the inventive method of a rolling operation.Accordingly, there is achieved just as good a welding of the inner pipesas with successive operations, as long as the partial pressing in of thematerial does not have any appreciable influence upon the elongation orstretching of the material, in other words, if the relationship betweenthe total cross-section and the pressed-in cross-section portion remainsas large as possible.

Furthermore, even if a rolling operation is superimposed upon theinventive method, then this presupposes that the temperature at theinside of the material during pressing is maintained as high as possiblein order to achieve a positive fusing or welding together of the bubblesor the fissures, with a relatively small degree of deformation. Thismeans, however, that the material located at the inside and which isalmost liquid, possesses rather poor plastic properties and can be onlysubjected to small tensile loads. Therefore, too large an elongation atthe region of the solidification point, and up to approximately 150 C.therebelow, for certain qualities of material even lower than this,results in the formation of cracks or fissures at the inside of thematerial.

FIGS. 9 to 11 illustrate the mode of operation of the inventive methodin contrast to the previous prior art methods. After a conventionalrolling operation, the billet 11 according to FIG. 9', after one pass,has become approximately one-third longer and possesses onlyapproximately two-thirds of its original height mass (FIG. The internaldefects or flaws, such as the blowholes 2 of the thus processed billet16 are indeed somewhat pressed together, but on the other hand,elongated in the lengthwise direction. Because of too high temperaturesat the inside of the material or because of poor plasticity, transversefissures or cracks 12 can appear in the billet 16 as shown in theillustration of FIG. 10.

Now, FIG. 11 shows an ingot or block 17 after it has been treated orprocessed according to the inventive method. In contrast to the billetv16, as such has been illustrated after the rolling operation of theprior art technique in FIGS. 10 and 10a, this FIG. 11 shows apractically unchanged length for the in-got or block 17, because only aportion of its periphery has been pressed in. The previously presentinternal defects or flaws have not been elongated in the lengthwisedirection, rather the material flow which has been forced toward theinside has resulted in a pressing together of the material associatedwith a welding together of such material, and therefore, in a removal ofthe internal flaws. Since during the pressing operation, undertaken withthe inventive method, practically no elongation or stretching of thematerial occurs, also no transverse fissures or cracks appear. When thetemperature at the inside of such an ingot =17 has dropped to a valuewhich is acceptable for a normal rolling operation, then the rollingoperation can, of course, take place with a standard succession ofpasses or rolling program.

The inventive method can, as already mentioned, be carried out with anumber of different types of tools, or apparatuses, for instance, withpress dies or tools, or profiled rollers, which stepwise or in oneworking operation carry out the pressing operation, and for whichpurpose so-called oscillating presses or hydraulic presses or rollermills of different constructions can be effectively employed.

During stationary casting the method can be considerably automated. Theingots or the like, in order to maintain the temperature suitable forthe pressing and-welding together of the material, are removed at theproper time from the molds or forms, and placed beneath the press toolor between the rollers, whereby there can be used a table roller orroller bed. The sequence of operation of the press tool or roller millcan, of course, occur completely automatically with the aid ofconventional control devices, terminal switches, photoelectric cells orthe like.

If the pressing-in devices of the invention are used in conjunction witha continuous casting installation, then they are preferably mountedafter the sprayingor cooling station. They can be of completely simpleconstruction since no particular infeed and withdrawal devices arerequired. It is sufficient to use profiled rollers, press tools, hammersand so forth which, if desired, can be synchronously moved during thepressing-in operation together with the strand. The deformation of thestrand necessary for the further processing can occur subsequently,before or after the cutting of the strand into the desired lengths. Inso doing, however, the internal temperature of the strand should havedropped to a value suitable for a normal rolling operation.

In the figures and in the description of the invention, the inventivemethod has been generally described in conjunction with a cast ingot orblock. Naturally, other types of cast pieces, for instance cast billets,slabs, blooms, blanks, and so forth can be deformed or worked by meansof the inventive technique or method. The cast piece can be, in thiscase, an endless strand or a piece which has been 'cut from the strandwith the help of suitable gas burners or cutters.

It should be apparent from the foregoing detailed description that theobjects set forth at the outset to the specification have beensuccessfully achieved.

Accordingly, what is claimed is:

1. Method for eliminating or at least reducing the internal flaws ofsemifinished products, especially in cast ingots, blooms, blocks, slabs,billets, or the like, comprising the step of exerting a pressing forceat only a portion of at least one side surface of the semifinishedproduct, and compressing by means of said pressing force the innerportions of the semifinished product at such time as such inner portionsare at a temperature below the solidification temperature therefor, andsaid inner portions having substantially solidfied with the trappedgases already having escaped to form cavities and shrinkage havingoccured, and the walls of any existing cavities having not yet oxidized,so that the cavities are welded shut and the portions of thesemifinished product which have not been subjectedto the pressing forceprovide resistance against a change in shape of the semifinishedproduct, and therefore, at least partially prevent an elongation of suchsemifinished product.

2. Method as defined in claim 1, including the steps of retaining insubstantially form-locking manner the partial surfaces of thesemifinished product which have not been subjected to the pressingforce.

3. A method as defined in claim 1, including the step of combining thepressing operation with a rolling operation.

4. Method for eliminating or at least reducing the internal flaws ofsemifinished products, especially for closing the cavities ofcontinuously cast semifinished products, comprising the steps ofexerting a pressing force at only a portion of at least one side surfaceof the semifinished productin a direction towards said cavities at leastat such time as the core portion of the continuously cast semifinishedproduct is at a temperature below the solidification temperaturetherefor, and said core portions having substantially solidified withthe trapped gases already having escaped to form cavities and shrinkagehaving occurred and such core portion is no longer molten, said pressingforce being exerted during continuous casting of the semifinishedproduct and at a location thereof where such semifinished product duringthe casting operation has just solidified.

5. The method as defined in claim 4, wherein said 7 8 pressing force isexerted by subjecting the semifinished FOREIGN PATENTS product to arolling operatlon 1n its lengthwise direction. Ad. 58,498 7/1953 FranceReferences Cited 625,127 3/1927 Australia 29-5263 UNITED STATES PATENTS5 MILTON S. MEHR, Primary Examiner 3,307,230 3/1967 Goss 164-282X 13,483,915 12/ 1969 Schneckenburger et a1. CL

16482X 609,693 8/1898 McDonald 29-5263 10 16 82; 29- 2 1,349,733 8/1920Read 29526.3

